This invention relates to a blow tube construction of the kind used in a foundry to inject particulate material and gas into a mold to form a core.
Blow tubes of the kind with which the invention is concerned are used in high volume cold box and hot box core making machinery.
In common use in the foundry industry are blow tubes comprising a steel tube having a rubbery tip that removably snaps over one end of the tube. The rubbery tip creates a seal between the blow tube and the core box and minimizes wear at the tube/core box interface. Some difficulties exist with this type of blow tube. For example, the tips sometimes separate from their tubes, even though they may be changed frequently, thereby causing down time and labor for tip replacement. This can be a major economic issue.
There is no way to determine for certain when a tip is about to separate from its blow tube. Accordingly, some operators change them at the beginning of every shift so they will be less likely to separate during the shift. Other operators change the tips at regularly scheduled intervals, but they often separate anyhow thereby adversely affecting the production of cores and causing sand to be blown to areas other than into the mold.
Another problem with the use of metal blow tubes used to deliver sand from a blow plate to a core box is the damage that may result to the blow tube, or blow plate, or the core box when any misalignment between the blow tube and the core box occurs. In those instances in which a blow tube is misaligned with the inlet port to a mold cavity damage can occur to the blow tube, the core box, the blow plate or all of these components, thereby resulting in the necessity of making costly repairs, as well as rendering the machinery inoperable during the time required to make the repairs.
A further disadvantage of metal and non-elastic blow tubes is that, following the filling of a mold with sand, the passage of sand through the blow tubes is interrupted while the blow plate and core box are separated. In those instances in which the sand to be injected into a mold is mixed with a binder, as frequently is the case, bonding between sand particles occurs when the sand is at rest, i.e., not flowing through the blow tube. When such bonding occurs it is not uncommon to have to discontinue core production until such time as the bonded sand clumps are removed from a clogged blow tube or the blow tube itself is replaced.
A principal object of the invention is to provide a blow tube which overcomes or greatly minimizes the objectionable characteristics referred to above.
A blow tube constructed in accordance with a preferred embodiment of the invention comprises an elongate, tubular body having a bore extending axially therethrough. At one end of the body is a coupling ring which enables the body to be secured to an orifice plate forming part of a sand container and overlying a core box having a port plate through which sand from the container may enter the mold for the purpose of forming a sand core. The blow tube body is formed of a rubbery, elastic, resilient material which is capable of compensating for misalignments which may occur between the sand outlet of the sand container orifice plate and the inlet port of the core box port plate. That end of the blow tube which is adapted to enter the inlet port to the core box is externally tapered so as to facilitate a seal being effected between the tip of the blow tube and the inlet port.
Sand conventionally is delivered to the mold via a blow tube under the influence of both gravity and pressurized gas such as air. The pressurized gas enables the sand to be packed more densely and uniformly in the mold. The packing is improved with a blow tube according to the invention by tapering the blow tube bore in a direction toward the discharge end of the latter so as to accelerate the rate at which sand is discharged from the blow tube and increase the density of the sand in the mold.
The elasticity of the material from which the blow tube is made is such that, in the event the bore becomes clogged by bound-together sand particles following periods during which the sand is at rest in the blow tube, the pressurized gas will cause the body of the blow tube to expand radially so as to facilitate separation of the particles of the clogged sand from one another and be discharged. The effectiveness of the compressed gas in these circumstances is increased by the tapering of the bore through which the sand passes.
When a mold cavity is filled to the desired extent with sand it is sometimes desirable to tamp the sand to solidify the core. For this purpose a tamping pin similar in many respects to the blow tube is provided and comprises a tubular body having a bore extending axially therethrough and terminating at one end in a coupling ring similar to that provided on the blow tube. At the other or free end of the tamping pin body is a rigid sleeve fitted into the bore and such sleeve accommodates a grate which is flush with the free end of the pin. The grate has passages through which air or other gas may flow to react with whatever binder is mixed with the sand.
The tamping pin may be vibrated vertically to effect tamping of the sand in the mold. Accordingly, the grate is one which is so constructed as to be capable of applying a compressive force on the sand as the pin is vibrated.